Why Does Time Go Only One Direction? 

It seems that the arrow of time moves only from the past to the future, never from the future to the past. Why is that? There are several theories, from the obvious to the inscrutable, that attempt to explain this. In this episode I cover the thermodynamic, the cause-and-effect, the wave expansion, the cosmic, and the quantum theories for the arrow of time.
None of them, I hate to say, bode well for the prospects of time travel.